What is the right expression when saying: "I am grateful"?
Do we say "I am grateful to you" or "I am grateful for you? Or are there other expressions?
What is the noun of this adjective "grateful?
I agree with Jasper; the main way to express a thankful spirit is with a simple "Thank you."
That said, the choice of prepositions can create some distinctions about gratefulness (or thankfulness).
I am grateful for you
means:
I am thankful that I have you in my life (someone might say this about their spouse, for example).
I am grateful to you
means:
I am thankful about something you did to help me; I feel indebted to you for your kindness.
"Thank you" is the most common way of expressing gratitude.
"I am grateful" is a valid statement. It is commonly used when "saying grace" (making a prayer before eating). A typical usage is "We are grateful for these blessings you have bestowed upon us", or "We are grateful for the company of our friends Bill and Jane on this special occasion."
In the sentence "I am grateful", the subject is "I"; "grateful" describes the subject.
Some similar expressions:
Each of the previous three expressions can be followed by "for" and a description of the favor that you are thankful for. For example, "How can I express my gratitude for saving my life?"
Saying "I am grateful for you" is ambiguous. The most likely meaning follows the pattern I just described -- "I am grateful" (to God?) "for" the chance to have "you" in my life. It could also mean "I am grateful" (to God?) "for" the blessings that have been bestowed upon "you".